This invention relates to controlled release administration of pharmaceuticals.
It is desirable in the treatment of certain diseases of veterinary and/or human medical interest, such as, for example, certain infections or tumors, to be able to deliver a pharmaceutical agent to a particular site in the body of the animal or person suffering from the disease and to provide for such local delivery at levels at least high enough to provide an effective dose over a sustained period of time.
Mastitis is one such disease. Mastitis is an infection of the breast or udder of a mammal, usually caused by a bacterial invasion. Mastitis in dairy animals can cause poor milk quality, a reduction in milk production, or even loss of the animal.
Relief from an infection can be provided, for example, by administering an antibiotic to the animal. Administration of the antibiotic by a single injection at the site of the infection can result in a high initial level of the pharmaceutical agent followed by a rapid decline in level to a level eventually of very little pharmaceutical agent, even where, as may be the practice, the antibiotic is suspended in an ointment base intended to provide a s low release of the antibiotic at the site in the body.
Conventionally, the antibiotic can be kept above a level that provides an effective dose by administering an initial loading dose followed by repeated maintenance doses. Thus, using conventional means of administration, maintaining a dose sufficient to combat an infection successfully or to provide prophylaxis against recurrent infection can require repeated injection and can result in problems of pharmaceutical overdose. At excessively high levels, an antibiotic can irritate the tissues at the site of administration, and can impede the phagocytic activities of the leucocytes, which normally help to remove invading bacteria from the infection site.
In the case, for example, of bovine mastitis the antibiotic conventionally is administered by infusion or injection of a quantity of antibiotic directly into the udder. Following such conventional administration, the antibiotic can persist in the udder and can appear in the milk at levels unacceptable for human consumption for some time beyond the time required for clearing the infection. At levels lower than an effective dose, which can nevertheless result in unacceptable levels in the milk, the antibiotic fails to produce the desired therapeutic effect.